A redundant array of inexpensive disks (RAID) apparatus is known in which a plurality of hard disk drives (HDDs) are combined to constitute a RAID group. In such a RAID apparatus, even if some disk fails, data stored therein may be guaranteed. Where a RAID apparatus includes a hot spare disk (hereinafter referred to as “HS”), the HS is temporarily used as a disk of the RAID group. When the failed disk is replaced, the RAID apparatus restores a state before the occurrence of the failed disk.
The restoration of the RAID apparatus is performed, for example, in the following procedure.
(1) A disk constituting a RAID group (the disk may be referred to as “member disk”) fails.
(2) Data of the failed disk is generated from normal member disks and written into an HS (this may be referred to as “rebuild”).
(3) The failed disk is replaced, and the data of the HS is written back into the new member disk (this may be referred to as “copy back”).
When a presage of failure in an HDD is detected, data is copied into the HS in advance before the HDD is decoupled from the RAID apparatus (this may be referred to as “redundant copy”) to secure the redundancy of the RAID group.
Related techniques are disclosed in, for example, Japanese Laid-open Patent Publication No. 08-249133, Japanese Laid-open Patent Publication No. 2006-268502, and Japanese Laid-open Patent Publication No. 2010-128773
In a case where an original member disk fails during a rebuild process or a redundant copy process, the data of the failed disk may be unable to be generated, resulting in occurrence of data loss.
The time required for rebuilding and redundant copying depends upon the rotational speed and the capacity of the HDD. Therefore, as the rotational speed of the HDD decreases or as the capacity of the HDD increases, the time required for the process increases and the possibility increases that a failure may occur in a member disk during a rebuild process or a redundant copy process.